Early trickle, then nothing, then mid-morning warblers

Heysham Obs
Whats the theory on clear mornings?  Birds move until they are tired, then land late morning(ish), hence the best time for rare warblers and the like is often midday e.g. Walney - althought the theory here is that they might filter down the island

Heysham office and area (Pete)
0600-0700
Grey Wagtail - 3 SE (two ringed)
Meadow Pipit - 5 SE
Chiffchaff - 2 grounded & ringed
0800-1100ish
"Nothing" stirred or flew over
1100 onwards
Swallow - 27SE
House Martin - 5 SE
Grey Wagtail - 1 SE
Meadow Pipit - 2 SE
Blackcap - 4 ringed
Whitethroat - one ringed
Willow warbler - one ringed
Chiffchaff - at least two new birds
Lesser Whitethroat - one ringed, one retrapped from a week ago

Middleton NR (Alan)
Similar situation with hardly anything moving between the first light trickle and about 0930hrs
Grasshopper Warbler - 1CY ringed
Lesser Whitethroat - 4 ringed - all after 1000hrs
Whitethroat - one ringed late morning
Blackcap - 2 ringed
Pied Wagtail - one ringed!
Grey Wagtail - 3 ringed early on, the only ones recorded
Quite a few Swallow & Goldfinch ringed